Moisture management of textiles

ABSTRACT

Moisturing management indexes are determined for a textile sandwiched between two plates. Electrical conductors arranged in concentric opposing pairs are used to measure changes in electrical resistance of the fabric. A quantity of water (or other chosen liquid) is poured down a guide pipe and changes of resistance measured against time. From this data, specific indexes are determined, in a repeatable fashion, and used for determining moisture management characteristics of the fabric.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to moisture management of textiles.

[0003] 2. Description of Prior Art

[0004] In the design of textile fabrics, or layers of fabrics as used indiapers, say, the manner in which moisture is absorbed, distributed andevaporated from the fabric is varied by changing the materials and/orthe structure. For various fabric applications in rainwear, sportsequipment, medical dressings, incontinent pads and so forth, differentproperties or combinations of properties or characteristics arerequired. Broadly stated, such applicable properties and characteristicsare already known or empirically provided in practice. However, nosatisfactory testing methods or equipment are available forscientifically measuring or testing fabrics, especially for complexfabrics.

SUMMARY OF THE INVENTION

[0005] It is an object of the invention to overcome or at least reducethis problem.

[0006] According to one aspect of the invention there is provided amethod of determining moisture management indexes of a planar textilefabric piece by pouring a quantity of liquid onto an area of an uppersurface of the piece, measuring changes in electrical resistance throughthe piece and within a plurality of laterally disposed electricallyenclosed areas of upper and lower surfaces of the piece, and, based onthe electrical resistances, computing indexes:

[0007] (i) S₁ and S₂, being accumulated liquid absorption of the uppersurface of the piece and the lower surface of the piece, respectively;and

[0008] (ii) H, being maximum difference of water content at the upperand lower surfaces.

[0009] The method may include computing an index R, the ability of thepiece to transport liquid across a thickness, being equal to a ratio$R = \frac{S_{2} - S_{1}}{S_{1}}$

[0010] The method may include computing indexes K₁ and K₂, the initialliquid absorption speeds at the upper and lower surfaces, respectively.

[0011] The method may also include computing indexes α₂ and α₂, thedrying rates at the upper and lower surfaces, respectively.

[0012] According to another aspect of the invention there is providedequipment for computing specific indexes relating to moisture managementof a planar textile piece of fabric material comprising:

[0013] a pair of opposed plates having an array of corresponding exposedopposed electrodes displaced at intervals from one another to form pairsof electrodes between which a piece of fabric can be held,

[0014] means connected to the electrodes for measuring changes inelectrical resistance through the piece and developed laterally acrosselectrically enclosed areas of upper and lower surfaces of the piece,

[0015] means for recording those changes in electrical resistance withrespect to time, and

[0016] means for computing the indexes.

[0017] The electrodes are concentric electrical conductive ringsdisplaced about a central region.

[0018] The equipment may include means for adjusting separation of theplates so as to apply different pressure to a fabric piece supportedbetween the plates.

[0019] The electrodes may each be laid out rectangularly in plan overincreasing surface areas about a central region.

BRIEF DESCRIPTION OF DRAWINGS

[0020] Equipment for and methods of determining moisture managementindexes of a textile piece according to the invention will now bedescribed by way of example with reference to the accompanying drawingsin which:

[0021]FIG. 1 is a schematic side view of a part of the equipment;

[0022]FIG. 2 is a sectional side view of the equipment;

[0023]FIG. 3 is a plan view of one electrode plate of FIG. 1;

[0024]FIG. 4 is a graph of water content and time;

[0025]FIG. 5 is an another graph of water content and time;

[0026]FIG. 6 is a graph of relative water content against time forpolyester covered cotton fabric, fabric No. 1;

[0027]FIG. 7 is a graph of relative water content against time forpolyester covered cotton fabric, fabric No. 2;

[0028]FIG. 8 is a graph of 100% cotton knitted fabric, fabric No. 3;

[0029]FIG. 9 is a graph of 100% polyester knitted fabric, fabric No. 4;

[0030]FIG. 10 is a table of indices for fabrics No. 1 to 4; and

[0031]FIG. 11 is a schematic circuit for the equipment;

[0032]FIG. 12 is an alternative schematic circuit for the equipment;

[0033]FIG. 13 is a diagrammatic plan view of another electronic plate ofFIG. 1; and

[0034]FIG. 14 is a diagrammatic plan view of a further electrode plateof FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] Referring to the drawings, in FIGS. 1 and 2 a water guide pipe 10is provided above a pair of opposing plates 11 and 12, each plateincluding an array of six concentric electrical conductors 13 as shownin FIG. 3. A textile fabric piece 14 is positioned and held between theplates 11 and 12 for testing and is located in position by a centralconductor pin 15. Electric wires, not shown, are connected to eachopposing pair of conductors and voltages developed across the piece 14at each pair are monitored as required. The voltages representing theeffective resistance values enclosed areas of upper and lower surfacesof the fabric are collected by a sensing module. The sensing modulerecords the voltages, against time, for computing various indexes, asexplained below.

[0036] In use, a quantity of water, or other liquid as appropriate, suchas brine or urine solution, is poured into the guide pipe. The waterflows onto a central region of an upper surface of the fabric piece andis absorbed by the fabric piece. Voltage measurements are recorded sothat indexes, which correspond to the quantity and the rate that thewater passes through and laterally along the fabric piece from thecentral region, can be computed.

[0037] These voltages, V are measured according to a schematic circuitshown in FIG. 10 (where R is a fixed 1 megaohm resistor).

[0038] Thus, $V_{i} = {V_{i} = \frac{V_{o} \cdot R_{f}}{1000 + R_{f}}}$

[0039] where R_(f) is the resistance of the fabric, using an 1000 ohmfixed resistor.

[0040] R_(f) is a known function of moisture content so that moisturecontent can be expressed as:

[0041] M_(i)=constant ${x = \frac{V_{c} - V_{i}}{V_{i}}},$

[0042] where V_(o) equals the battery (i.e. applied) voltage, and V₁equals the voltage between the innermost pair of conductors. The totalof the water content U can be computed at each surface according to$U = {\sum\limits_{i = 1}^{6}\quad {M\quad i}}$

[0043] (if there are six pairs of conductors)

[0044] In FIG. 4, the graph shows a typical graph of U against time inseconds for the upper (upside) and lower (bottom side) surfaces of thefabric. An initial slope of each curve represents initial waterabsorption rates (K) at the two surfaces, so that K₁=tan A, and K₂=tanB.

[0045] The maximum difference of water content at the two surfaces H isgiven according to the expression:

H=U _(TOP)(max)−U _(bottom)(max)

[0046] The graph in FIG. 5 is used to compute the accumulated content(S) and the relative difference (R) in accumulated water content betweenthe upper and lower surface of the textile piece.

[0047] Thus S₁=∫U_(Top)dt and S₂=∫U_(bottom)dt and$R = \frac{S_{2} - S_{1}}{S_{1}}$

[0048] FIGS. 6 to 9 are graphs of U plotted against time for differentmaterial fabric pieces.

[0049] For each pouring of a quantity of water, the moisture contentwill increase to a maximum value, and then the moisture content startsto decrease expotentially due to evaporation. The water content (U)decreases according to

U=Ax exp(−α.t)

[0050] It will be appreciated that α can be derived for both surfaces.

[0051] Overall moisture management capacity of a fabric, which indicatesthe fabric's capability of quick liquid absorbency, one-way moisturetransport and quick dry, is defined as:${OMMC} = {{0.25 \times \frac{K_{2} - {\overset{\_}{K}}_{2}}{\sigma_{k2}}} + {0.5 \times \frac{R - R}{\sigma_{R}}} + {0.25 \times \frac{\alpha_{2} - \overset{\_}{\alpha}}{\sigma_{\alpha \quad 2}}}}$

[0052] The larger the OMMC is, the higher the overall moisturemanagement capability of the fabric is.

[0053] Thus, the described equipment and the methods provide meaningfulindexes that are based on measurements of voltages against time when atextile fabric piece is tested using a quantity of suitable liquid.Although resistance measurements have been used in the past fordetermining fabric characteristics, they have not made use of transversemigration of liquid in the fabric or provided useful repeatable indexesrelating to moisture management. Known tests include dropping water ontoa textile piece surface and visually observing its migration. Suchobservations are unreliable, especially if the fabric is dark-coloured,or in situations when the water spreads very quickly. By contrast,embodiments of this invention can provide accurate, repeatable andmeaningful test information for each single fabric piece, or formulti-layered fabric pieces, if required.

[0054] In addition, the plates 11 and 12 may be arranged to berelatively movable or adjustable in a manner to apply differentpressures between the electrodes against the fabric pieces, or layers offabric pieces, during testing. Clearly it is important for someapplications or uses to determine what chances in the moisturemanagement of the textile pieces will occur due to applied pressure.Such information is useful for fabric materials that will be subjectedto changes, in such pressure, during use.

[0055] The Table n FIG. 10 shows the results of testing four differentfabrics. It can be readily deduced from the Table that all four fabricshave a relatively good moisture absorption rate, although fabric No. 1is the best. In terms of one-way transport of water, Fabric No. 2appears to be better than the other fabrics initially. Over a longerperiod however, Fabric No. 1 is better than Fabric No. 2, Fabric No. 3and Fabric No. 4 show in effect no one-way transport capability. Interms of drying speed, Fabric No. 1 and Fabric No. 2 are similar,showing good quick-dry behaviour. Meanwhile, Fabric No. 3 shows poordrying behaviour and Fabric No. 4 shows no sign of drying within thetest period. In term of overall moisture management as shown by OMMCvalues, Fabric No. 1 has the best performance, followed by Fabric No. 2.Fabric No. 3 and Fabric No. 4 show unsatisfactory performances.

[0056] Thus it can be immediately deduced that, for example, Fabric No.3 and No. 4 would be unsuitable for sports clothing generally, althoughsuch fabrics may be suitable and advantageously used for inner liners ofoutdoor athletic clothing. It can also be deduced that, for example,Fabrics No. 3 and No. 4 would be unsuitable for sportswear andincontinent products for use next-to-the skin, as such Fabrics will notkeep the skin dry and comfortable when liquid is discharged from thebody. Fabric No. 2 will perform better than Fabric No. 3 and No. 4 forsportswear and incontinent products, as Fabric No. 2 has relatively gooddifferential transport capability and will quickly dry. Fabric No. 1will be the best for sportswear and a next-to-skin layer of incontinentproducts, as it has the best moisture management capability andindividual aspects of performance in terms of differential liquidtransport, water absorbing and drying rates.

[0057] In another preferred arrangement for computing moisturemanagement indexes, the fixed resistor in FIG. 11 is chosen as 47kΩ(R_(ref)), thus if R_(f) is the resistance of the fabric:$V_{OUT} = {V_{DD} \times \frac{R_{f}}{{47k} + R_{f}}}$

[0058] R_(f) is a known function of moisture content so that moisturefunction (M) can be expressed as:${Mi} = {\frac{1}{{Ai} \cdot R_{f}} = \frac{V_{DD} - V_{OUT}}{{{Ai} \cdot 47}{k \cdot V_{OUT}}}}$

[0059] where V_(DD) equals the battery (i.e. applied) voltage, andV_(OUT) equals the voltage between a pair of conductors. The total ofthe water content at each surface can be computed (if there are sixpairs of conductors) as:$U_{TOP} = {{\sum\limits_{i = 1}^{6}\quad {M_{TOPi}\quad {and}\quad U_{Bottom}}} = {\sum\limits_{i = 1}^{6}\quad M_{Bottomi}}}$

[0060] Maximum Absorption Rate

[0061] In FIG. 4, the graph shows a typical graph of U against time inseconds for the upper (upside) and lower (bottom side) surfaces of thefabric. The maximum slope of each curve represents the maximum waterabsorption rates (S) at the two surfaces, so that

S _(TOP)=Maximum [slope(U _(TOP))], and

S _(Bottom)=Maximum [slope(U _(bottom))]

[0062] One Way Transport Capability

[0063] The graph in FIG. 5 is used to compute the one way transportcapability (R) on the basis of the difference in accumulated watercontent between the upper and lower surface of the textile piece:

R=[Area(U _(bottom))−Area(U _(TOP))]/Total Testing Time

[0064] The graphs of U plotted against time in FIGS. 6 to 9 fordifferent material fabric pieces are used as before.

[0065] Wetting Time

[0066] Wetting time (W_(t) and W_(b)) is defined as time when the slopeof total water content (U_(TOP) or U_(bottom)) become greater thanTan(15°) for the top and bottom surfaces respectively.

[0067] Maximum Wetted Radius (WR)

[0068] Maximum wetted radius (WR_(top) and WR_(bottom)) is defined asmaximum wetted ring radius at the top and bottom surfaces, where theslope of total water content (M_(topi) or M_(bottomi)) become greaterthan Tan (15°) for the top and bottom surfaces respectively.

[0069] Spreading Speed (mm/sec)

[0070] Spreading speed (SS_(top) and SS_(bottom)) is defined asSS=WR/t_(wr), where t_(wr) is the time to reach the maximum wetted ringfor the top and bottom surfaces respectively.

[0071] This other preferred arrangement is more useful in an industrialapplication. The set of 9 indexes and equations are able to provide moreconvenient and more meaningful results for practical usage. Wetting time(W) can be compared with a traditional drop test. The equations forcalculating maximum absorption rate (S) and one way transport capability(R) are more conveniently applicable to software replication. Maximumwetted radius (WR) and spreading speed (SS) provide additionalinformation on the geometric distribution of liquid moisture in thefabrics.

[0072]FIGS. 13 and 14 show other suitable configurations for theelectrodes 13. The configurations enable the changes of effectiveresistance to be sensed, by measuring voltages, in the same manner asbefore, within a plurality of enclosed areas of the upper and lowersurfaces of the fabric. The electrodes in FIG. 13 are each laid outrectangularly in plan and, in FIG. 14 extra ‘diagonal’ electrodes areprovided to enable the effective resistance of extra or differentelectrically enclosed surface areas to be measured.

1. A method of determining moisture management indexes of a planartextile fabric piece by pouring a quantity of liquid onto an area of anupper surface of the piece, measuring changes in electrical resistancethrough the piece and within a plurality of laterally disposedelectrically enclosed areas of upper and lower surfaces of the piece,and, based on the electrical resistances, computing indexes (i) S₁ andS₂, being accumulated liquid absorption of the upper surface of thepiece and the lower surface of the piece, respectively; and (ii) H,being maximum difference of water content at the upper and lowersurfaces.
 2. The method according to claim 1, including computing anindex R, the ability of the piece to transport liquid across athickness, being equal to a $R = \frac{S_{2} - S_{1}}{S_{1}}$


3. The method according to claim 1, including computing indexes K₁ andK₂, the initial liquid absorption speeds at the upper and lowersurfaces, respectively.
 4. The method according to claim 1, includingcomputing indexes α₂ and α₂, the drying rates at the upper and lowersurfaces, respectively.
 5. Equipment for computing specific indexesrelating to moisture management of a planar textile piece of fabricmaterial comprising: a pair of opposed plates having an array ofcorresponding exposed opposed electrodes displaced at intervals from oneanother to form pairs of electrodes between which a piece of fabric canbe held, means connected to the electrodes for measuring changes inelectrical resistance through the piece and developed laterally acrosselectrically enclosed areas of upper and lower surfaces of the piece,means for recording those changes in electrical resistance with respectto time, and means for computing the indexes.
 6. The equipment accordingto claim 5, in which the electrodes are concentric electrical conductiverings displaced about a central region.
 7. The equipment according toclaim 5, including means for adjusting separation of the plates so as toapply different pressure to a fabric piece supported between the slates.8. The equipment according to claim 5, in which the electrodes are eachlaid out rectangularly in plan over increasing surface areas about acentral region.